This invention relates to a process for the electrooxidation of methanol to formaldehyde and methylal.
Formaldehyde is an important starting material for the production of certain polyacetal resins. It can be produced by the partial oxidation of methanol with air or oxygen in the presence of a variety of catalysts and under a variety of conditions. In some cases, methanol and formaldehyde formed in the process react further to give methylal, CH.sub.2 (OCH.sub.3).sub.2 ; furthermore, formaldehyde often is in the same process oxidized in part to formic acid, which may again react with methanol to give methyl formate. Formation of methylal is not considered to be particularly detrimental to the production of formaldehyde because methylal can be readily hydrolyzed back to methanol and formaldehyde, as is well known in general for acetals and ketals. This catalytic process, in its various forms, is currently used to produce formaldehyde commercially. Nevertheless, it has the drawback of producing one mole of water for each mole of formaldehyde formed. This requires a rather complex and costly procedure for removing water from the formaldehyde produced. In addition, residual formaldehyde still present in the waste water must be removed before this water can be safely discharged.
Electrochemical oxidation of ethanol to acetaldehyde in a fuel cell arrangement is described in U.S. Pat. No. 4,457,809 (to Meshbesher).
Simultaneous electrochemical reduction of a mixture of benzene and methanol in the presence of tetrabutylammonium perchlorate to phenol in the cathode compartment and oxidation to methylal in the anode compartment in a cell equipped with an ionic transfer membrane is reported in U.S. Pat. No. 4,732,655 (to Morduchowitz et al.).
Electrocatalytic oxidation of methanol to methyl formate and methylal on a platinized solid polymer electrolyte membrane was reported by Otsuka et al. in Applied Catalysis, 26(1986) 401-404. The authors describe a process that occurs without either a solvent or a liquid electrolyte.
It is desirable to be able to produce formaldehyde and/or methylal in a selective manner and in an industrially satisfactory yield in a process that requires or produces a smaller amount of water than is produced in the conventional catalytic oxidation processes.